How to check whether a string contains a substring in Ruby?

I have a string variable with content as follows:

varMessage =   
            "hi/thsid/sdfhsjdf/dfjsd/sdjfsdn\n"


            "/my/name/is/balaji.so\n"
            "call::myFunction(int const&)\n"
            "void::secondFunction(char const&)\n"
             .
             .
             .
            "this/is/last/line/liobrary.so"

in above string i have to find a sub string i.e.

"hi/thsid/sdfhsjdf/dfjsd/sdjfsdn\n"


"/my/name/is/balaji.so\n"
"call::myFunction(int const&)\n"

How can I find it? I just need to determine whether the substring is present or not.